To solve the issue, I made following changes in OBSERVATION state.

1. Set offset of 0.097 at K1:BPC-YAW_ETMY_INF_OFFSET.
2. Increase gain of BPC by a factor of 10 by changing the gain at K1:BPC-{PIT,YAW}_ETMY_INF_GAIN from 1 to 10.
3. Change demod phase of ETMY YAW BPC for swapping the sign of the signals.

To achieve above modification without affecting the other states, I modified several states in the ASC_LOCK guardian as follows:

DOWN state:

Turn off OFFSET switch of K1:BPC-PIT_ETMY_INF filter bank.
Also, set the gain of 1 at K1:BPC-{PIT,YAW}_ETMY_INF_GAIN.

SET_BPC_FREQ_FOR_OBSERVATION state:

Change setting demod phase at K1:BPC-PIT_ETMY_DEMOD_PHASE from 47 to -133.
Turn on offset switch of K1:BPC-YAW_ETMY_INF filter bank.
Change gains at BPC-{PIT,YAW}_ETMY_INF_GAIN from 1 to 10.